ODC1 and breast carcinoma: To investigate the regulatory role of polyamine anabolism in chemotherapy‐induced BCSC enrichment, we generated shRNA‐mediated non‐targeting control (NTC), ODC1, or SRM knockdown subclones of breast cancer cells (Figure 2H; Figure S2I, Supporting Information), and found that knockdown of ODC1 or SRM abrogated paclitaxel‐induced increases of ALDH+ cell population (Figure 2I; Figure S2J, Supporting Information), and decreased BCSC P‐Sig expression and increased BCSC N‐Sig expression (Figure S2K, Supporting Information).